Growers of fruit and vegetables in areas where occasional frost might pose a hazard to the crops are faced with the need to prevent such hazards. A number of methods for preventing or reducing crop damage from frost spells have been or are in use. Such methods employ suitable fires placed upwind from the growing area, or methods for agitating the air in the growing area with motor driven propellers mounted on masts. Such methods have the drawback of being expensive and uncertain and require bulky, space consuming equipment.
The present invention discloses a system which makes use of directed beams of electromagnetic energy that may be directed toward trees or plants that need protection.
Fields of electromagnetic energy have been known and used for heating purposes for a long time. Examples are industrial heating of materials to be joined by exposing them to an intense field of high frequency energy which due to dielectric losses in the material, causes most of the high frequency energy to be absorbed in the material and there converted into heat. Another example is the microwave oven which is now widely used for heating of food. In a microwave oven, electromagnetic energy of a very high frequency, typically in the frequency range of 0.95 to 5 gigahertz is injected into an enclosure containing the food to be heated.
U.S. Pat. No. 4,256,944 by Brandon, issued Mar. 17, 1981 describes a system for thawing bulk particulate material by means of powerful microwave beams directed toward the material to heat and thaw it.
U.S. Pat. No. 3,461,260 by Bremer, issued Aug. 12, 1969 describes a microwave oven connected to a source of microwave energy.
The present invention discloses a method for prevention of frost damage to agricultural crops by producing a beam of microwave energy that may be directed toward particular trees or areas or toward stands of fruit or vegetables.
It is well known, from the fields of physics and electromagnetic science that electromagnetic waves by suitable antennas may be concentrated and directed as beams. Normally, the larger the antenna in relation to the wavelength of the electromagnetic energy, the more narrowly the beam may be concentrated. Microwaves which generally fall in the range of wavelength from 2 to 20 centimeters can be economically concentrated into directed beams with antennas which are physically generally five or more times greater than the wavelength of the microwave energy in question. In other words, antennas that have physical dimensions greater than from 20 to 100 centimeters or greater for good directability may be employed.
It has been found by experience and analysis that reflecting antennas with the shape of a paraboloid reflector are especially well suited for use as microwave antennas.
The present invention discloses a system for frost protection of trees and plants during cold periods of time. It uses a source of microwave energy connected to a directional antenna, which may be directed toward trees or plants to generate enough heat energy in the tissue of the leaves and fruits to prevent freezing.
It is preferable to employ microwave energy of a wavelength that is absorbed to a high degree by water and the juices of plants and fruits, so that the energy is dissipated mostly in those parts of the plants. A frequency of about 3 gigahertz is believed to be useful with 3 results at about 2.45 gigahertz as seen in microwave oven technology and 1.6 gigahertz as seen in meteorological measurements.
It is therefore a major object of the present invention to provide a microwave system for frost protection of fruit trees and the like which employs a directed beam of microwave energy.
It is another major object of the invention to provide a microwave system for frost protection of fruit trees and plants that employs a directed beam of microwave energy that may be directed toward individual trees or plants under control of sequencing apparatus.
It is a further object of the invention to provide a microwave system for frost protection of fruit trees and plants, that is ambulatory so that one system may serve a larger area, or be deployed to areas that are more prone to frost damage than others.
It is a still further object of the invention to provide a microwave system for frost protection of fruit trees and plants that is economical and reliable in use.
It is still a further object of the invention to provide a microwave system for protection of fruit trees and plants that is energy efficient.
It is still another object of the invention to provide a microwave system for frost protection of fruit trees and plants that may be readily fabricated using established methods of manufacture.